Sheave for use in an elevator system

ABSTRACT

An elevator sheave ( 20 ) includes a belt guiding surface ( 26 ) having a surface profile along at least a portion of the belt guiding surface. The surface profile preferably is defined by an n th  order polynomial equation where n is a number greater than 2. In one example, the reference point ( 40 ) is a central point along the width of the belt guiding surface ( 26 ). In one example, a central portion ( 42 ) of the surface profile preferably is aligned to be generally parallel with the central axis ( 34 ) of the sheave body. Some examples have curvilinear side portions ( 44,46 ) between the central portion ( 42 ) and the edges ( 28,30 ) of the sheave. Other examples also include second side portions ( 48,50 ) that have linear profiles.

FIELD OF THE INVENTION

This invention generally relates to elevator sheaves and moreparticularly, to a unique belt guiding surface configuration on anelevator sheave.

DESCRIPTION OF THE RELATED ART

Elevator systems are widely known and used. Typical arrangements includean elevator cab that moves between landings in a building, for exampleto transport passengers or cargo to different levels in the building. Aload bearing member, such as a rope or a belt typically supports theweight of the cab as it moves through the hoistway.

As the cab moves through the hoistway, the load bearing member typicallymoves over at least one sheave. In some instances the sheave is a drivesheave, which is coupled to a motorized mechanism for moving theelevator cab as desired. In other instances, sheaves are passive andmove responsive to movement of the load bearing member.

While elevator sheaves have been in use for a long time, there is a needfor an improvement in their design to maximize the longevity of theelevator system components, such as the load bearing member. Forexample, flat belts typically are subjected to overload stresses as thebelt moves over the sheave. Additionally, because the elevator sheaveaxis is typically not perfectly aligned with the supporting mechanismaxis, there is a tendency for the belt to move sideways along the sheaveas the sheave rotates. While crowned sheave surfaces have been used toimprove belt-tracking behavior, they have the associated drawback ofintroducing an overload in at least some of the cords in the centralregion of the belt. Coated steel belts in which a plurality of steelcords are imbedded in a polymer coating are particularly subject to suchstrain because those belts are designed to be axially very stiff. Thecords are not uniformly stressed, resulting in uneven loading.Additionally, conventional crown designs do not adequately accommodatetracking behavior under all circumstances.

There is a need for an improved elevator sheave design that optimizestracking performance of the load bearing member and reduces overallstress on the load bearing member. This invention addresses that needwhile avoiding the shortcomings and drawbacks of the prior art.

SUMMARY OF THE INVENTION

An exemplary disclosed sheave for use in an elevator system has a beltguiding surface that maximizes tracking capabilities while minimizingstress induced on the load bearing member.

An example sheave includes a sheave body that has a central axis aboutwhich the sheave rotates. A belt guiding surface includes a surfaceprofile extending along at least a portion of the belt guiding surface.The surface profile preferably is defined by an equation thatapproximates an n^(th) degree polynomial, of a distance from a selectedreference point on the belt guiding surface, where n is a number greaterthan 2.

In one example, the belt guiding surface includes a central portion thatis aligned parallel with the central axis of the sheave. Side portionson either side of the central portion preferably are defined by anequation that approximates an n^(th) degree polynomial of a distancefrom a selected reference point on the belt guiding surface, where n isany number. The latter example is particularly useful for embodimentswhere the width of the load bearing member or belt is greater thanone-half of the width of the belt guiding surface.

In another example, first side portions on either side of the centralportion are defined by an n^(th) degree polynomial. Second side portionsextend from the first side portions toward outer edges of the sheave.The second side portions in this example have a linear profile.Accordingly, a sheave designed according to this example provides threedistinct zones on each side of a plane of symmetry through a center ofthe sheave.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiments. The drawings thataccompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates an elevator sheave assembly designedaccording to an embodiment of this invention.

FIG. 2 is a partial cross sectional illustration of the embodiment ofFIG. 1.

FIG. 3 illustrates selected features of an embodiment of this invention.

FIG. 4 schematically illustrates another example embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 diagrammatically illustrates an elevator sheave assembly 20 wherea sheave body 22 cooperates with a load bearing member 24. The loadbearing member 24 in one example is a coated steel belt. The term “belt”as used in this description should not be construed in its strictestsense. An assembly designed according to this invention may accommodateflat belts, coated steel belts, or other synthetic core belts used inelevator systems. The term “belt,” therefore, should be construed in ageneric sense to include a variety of configurations of load bearingmembers useful in an elevator system.

The belt 24 is received upon a belt guiding surface 26 that extendsbetween edges 28 and 30 on the illustrated sheave. The raised edges 28and 30 are not included in another example sheave. The belt rides alongthe surface 26 as the sheave rotates about a central axis 34. The beltguiding surface preferably includes a surface profile along at least aportion of the width of the belt guiding surface. The surface profilepreferably provides an at least partially crowned surface along whichthe belt rides on the sheave. As can be appreciated from FIG. 2, thebelt guiding surface 26 includes a surface profile that extends in anaxial direction and is at least partially convex as seen in a radialcross section of the sheave 22.

In one example, the surface profile is approximated by a higher orderpolynomial equation. This equation may be expressed as y=|x^(n)| where nis a number greater than 2, y is along an axis perpendicular to thesheave axis of rotation 34 and x is a distance measured from a referencepoint 40 on the belt guiding surface 26 in a direction parallel to thesheave axis of rotation. In the illustrated example, the reference point40 is at a central location along the width of the belt guiding surface26.

The example surface profiles maximize the tracking behavior of the belt24 on the belt guiding surface 26 while minimizing the stresses on thebelt caused by the shape of the profile. The example surface profilesenhance tracking robustness because they maintain adequate spacingbetween the edges on a belt and the sides of the sheave.

In examples as shown in FIG. 3, where the width w of the belt 24 isgreater than one-half the width c of the belt guiding surface 26, thesurface profile preferably includes a flat central portion 42. Adistance between each point along the central portion 42 and the centralaxis 34 is equal in the illustrated example. In other words, the examplecentral portion 42 preferably is aligned entirely parallel with thecentral axis 34 of the sheave 22.

Side portions 44 and 46 of the surface profile preferably extend betweenthe central portion 42 and the edges 28 and 30 of the belt guidingsurface, respectively. Each of the side portions 44 and 46 preferably isapproximated by the equation y=x^(n) where n is any number. In theexample of FIG. 3, n=2. In one example, the surface 26 has varioussections with different n values. In another example, the surface 26 hasportions with different n values on each side of the center of thesurface 26 such that the surface 26 is asymmetric about the center.

A crown design as shown in FIG. 3 preferably is flat along the sectionof the top of the crown that cannot be accessed by the trailing edge ofthe belt 24. The width of the central portion 42 preferably is equal totwice the difference between the width w of the belt 24 and one-half thewidth c of the belt guiding surface 26 (e.g., 2×(w-c/2)). The distance findicated in FIG. 3 preferably is equal to w-c/2 (e.g., the distance fis one-half the width of the central portion 42 in this example).Therefore, whenever there is spacing between the edges of the belt 24and the edges 28 and 30 of the sheave, respectively, neither belt edgewill be on the flat central portion 42.

FIG. 4 illustrates another example where the belt guiding surface 26 hasa central portion 42 that is aligned parallel with the sheave axis ofrotation 34. First side portions 44 and 46 extend away from oppositesides of the central portion 42. In this example, the first sideportions 44 and 46 have a profile described by an n^(th) orderpolynomial, where n is any number. In one particular example, n isgreater than 2. In this example, the first side portions 44 and 46 donot extend all the way toward ends 28 and 30 of the sheave.

Second side portions 48 and 50 extend between the first side portions 46and 44, respectively, and the edges of the belt guiding surface 26. Inthis example, the second side portions 48 and 50 have a surface profilethat is linear. In the illustrated example, the belt guiding surface 26is symmetrical about a plane through a center of the sheave (i.e., avertical plane extending into the page).

In examples as shown in FIG. 4, the second side portions 50 and 48preferably are linear. Having a linear profile section near the edges ofthe belt guiding surface 26 maintains the tracking efficiency of anarrangement having a curved surface extending between the centralportion and the edges of the belt guiding surface 26. Having a linearprofile, however, reduces the effect of the curved surface that wouldtend to compromise the service life of the belt without limiting thetracking efficiency of the most outward portions of the belt guidingsurface 26. This is accomplished, in part, because the loads on theportions of the belt riding over the outermost portions of the beltguiding surface 26 carry significantly lower loads than the portions ofthe belt riding over the central portion 42 and the more central areasof the first side portions 44 and 46.

In the figures, transitions between portions of the guiding surfaces 26are somewhat exaggerated for illustration. In an example sheave, theguiding surface is machined from a single piece of material and presentsa continuous, uninterrupted surface across the entire sheave.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to what has been disclosed above may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this invention. The scope of legal protection given tothis invention can only be determined by studying the following claims.

We claim:
 1. A sheave for use in an elevator system, comprising: asheave body having a central axis and a crowned belt guiding surfaceincluding a selected reference point the crowned belt guiding surfaceincluding a surface profile extending in an axial direction along atleast a portion of the belt guiding surface, the surface profile definedas an n^(th) degree polynomial of a distance from the selected referencepoint on the belt guiding surface where n is a number greater than
 2. 2.The sheave of claim 1, including a central portion of the surfaceprofile that has a width and is aligned parallel to the central axis. 3.The sheave of claim 2, wherein the central portion is entirely equallydistant from the central axis.
 4. The sheave of claim 2, including firstside portions on opposite sides of the central portion, wherein thefirst side portions have a surface profile defined by the n^(th) degreepolynomial, and including second side portions extending from the firstside portions toward edges of the belt guiding surface, the second sideportions having a linear profile.
 5. The sheave of claim 2, wherein thecentral portion has a profile that is distinct from the n^(th) degreepolynomial profile.
 6. The sheave of claim 1, including a first edge ofthe surface profile spaced a first nominal distance from the centralaxis and wherein the reference point is spaced a second distance fromthe central axis that is greater than the first distance.
 7. The sheaveof claim 6, including a central portion of the surface profile having awidth and an equal distance to the central axis along the entire centralportion.
 8. An assembly for use in an elevator system, comprising: abelt having a width; and a sheave that supports the belt and isrotatable about a central axis as the belt moves, the sheave including acrowned belt guiding surface having a width that extends between edgeson opposite sides of the sheave, the entire belt guiding surface being asingle piece of material that presents a continuous, uninterruptedsurface, the belt guiding surface having a central portion that has awidth across which the belt guiding surface is aligned parallel to thecentral axis so as to be at least partially equidistant from the centralaxis, and side portions extending from the central portion towardcorresponding edges of the sheave that are curved relative to thecentral axis, wherein the width of the central portion of the beltguiding surface is equal to approximately two times the differencebetween the belt width and one-half the width of the belt guidingsurface.
 9. The assembly of claim 8, wherein the central portion extendsin opposite directions from a center point on the belt guiding surfaceand one-half of the central portion is on each side of the center point.10. The assembly of claim 8, wherein the side portions of the beltguiding surface each have a curvature defined by an n^(th) orderpolynomial of a selected reference point on the belt guiding surface.11. The assembly of claim 8 wherein the entire central portion isequally spaced from the central axis and the distance between thecentral portion and the central axis is greater than the distancebetween the central axis and any point along the side portions.
 12. Theassembly of claim 8 wherein the belt width is greater than one-half thewidth of the belt guiding surface.
 13. The assembly of claim 8 includingsecond side portions extending from the side portions toward thecorresponding edges of the sheave, the second side portions having asurface profile that is linear.
 14. A sheave for use in an elevatorsystem, comprising: a sheave body have a central axis and a crowned beltguiding surface including a selected reference point, the crowned beltguiding surface including a surface profile extending in an axialdirection along at least a portion of the belt guiding surface, thesurface profile having a central portion, first side portions extendingaway from opposite edges of the central portion toward correspondingedges of the sheave and second side portions extending away from thefirst side portions toward the corresponding edges of the sheave, thecentral portion having a width across which the surface profile has aparallel alignment with the sheave central axis, the first side portionshaving a curved profile and the second side portions have a linearprofile, wherein the first side portions have a surface profile definedas an n^(th) degree polynomial of a distance from the selected referencepoint on the belt guiding surface, wherein n is a number greater thantwo.
 15. The sheave of claim 14, wherein the entire central portion isequally distant from the sheave central axis.